1. Field of the Invention
The present invention relates to an automatic gain controlling method for controlling the variable amount of the gain according to the level of the received signal using an RSSI (Receive Signal Strength Indicator) that detects the electric field intensity of the received signal so as to convert the received signal as an analog signal into a digital signal. The present invention also relates to an automatic gain controlling apparatus corresponding to the automatic gain controlling method and a communication receiving apparatus having the automatic gain controlling apparatus.
2. Description of the Related Art
A conventional receiving apparatus for use with a radio communication system performs an automatic gain controlling process corresponding to the fluctuation of the level of the received signal.
In for example a CDMA mobile communication system of which a plurality of users use the same frequency, an RSSI that detects the electric field intensity of the received signal is used to control the variable amount of a gain varying unit disposed in a receiving apparatus so as to keep the level of a signal that is supplied to an analog/digital (A/D) converting unit.
However, in the conventional radio communication receiving apparatus, as shown in FIG. 1, the RSSI controls the gain varying unit so that the variable amount thereof is proportional to the input level as the level of the received signal. Thus, since the variable amount of the gain varying unit is controlled corresponding to information of the preceding slot of the received signal. Consequently, when the level of the received signal largely fluctuates, the variable amount of the gain varying unit becomes excessive. As a result, the automatic gain controlling process may not properly operate corresponding to the abrupt fluctuation of the received signal for fading, shadowing and so like.